Process for separating metals



NOV. 17, 1936. pERKlNS 2,061,251

PROCESS FOR SEPARATING METALS Filed July 25, 1954 2 Sheets-Sheet 1IIIIII 1' llil 1mg: 3

INVENTOR BY Zmqm 17% K ATTORNEY Nov. 17, 1936. M. F. PERKINS PROCESS FORSEPARATING METALS Filed July 25, 1934 2 Sheets-Sheet 2 INVENTORJg/z/1ZZeF/ rhkz ATTORNEY Patented Nov. 1?, 1936 PATENT OFFICE PROCESSFOR SEPARATING METAL Melville F. Perkins, Woodbridge, N. J., assignor toAmerican Smelting and Refining Company, New York, N. Y., a corporationof New Jersey Application July 25, 1934, Serial No. 736,896

13 Claims.

This invention relates to the separation and/or purification ofsubstances by liquation and distillation.

Among other features, the invention provides 5 a process forcontinuously effecting the removal of a lower boiling component as asubstantially pure vapor from a bath of material containing a higherboiling component by constantly maintaining the total content of thehigher boiling component of the bath ata low value throughout theprocess. The invention also provides for concentrating the higherboiling component while simultaneously removing the lower boilingcomponent vapor. The novel manner in which the low content of the higherboiling component of the bath is maintained is also a feature of theinvention.

For example, in treating spelter, the invention contemplatescontinuously and simultaneously distilling and liquating the spelter insuch manner that zinc is continuously distilled from a bath'whose leadcontent is maintained at a low value by continuous liquation, theprocess being readily accomplished in an appropriate furnace having twochambers or compartments connected with suitable passageways foreffecting intercirculation of metal between the chambers.

The present application is a continuation in part of the co-pendingapplication of Melville F. Perkins, Serial No. 627,589, filed August 5,1932.

Although the novel features which are believed to be characteristic ofthis invention will be particularly pointed out in theflclaims appendedhereto, the invention itself, as to its objects and advantages, and themanner in which it may be carried out may be better understood byreferring to the following description taken in connection with theaccompanying drawings forming a part thereof, in which Fig. l is a crosssection of a furnace embodying the principles of the invention.

Fig. 2 is a plan view in section of the same furnace on the line 2-2 ofFig. 1.

In the drawings accompanying and forming 45 part of this specification,certain specific disclosures of the invention are made for purposes ofexplanation, but it will be understood that the details may be modifiedin various respects without departure from the broad aspects of theinvention.

Referring more particularly to the drawings, a furnace is shown havingwalls I 0, H, 12 and I3, roof l4 and hearth 15, the latter resting onbase material I6. Insulation His provided to cover 55" the roof andwalls.

A common wall l8 extending .from the roof I 4 to the hearth I5 dividesthe-interior of the furnace into two chambers or compartments l9 and 20,which are connected by ports or passageways 2! and 22 extending throughwall l8. Fire 5 tubes 23 of suitable refractory material extend throughwalls 12 and I3 and chamber 20. Passageway 24 connects flue 26 withchamber I9 through port 25. Chamber I9 is provided with a charging port21 and tap hole 28, while cham- 10 bers l9 and 20 are provided withexits 29 and 30 respectively. A safety trap 3! is provided in the lowerportion of flue 26 by dam 32. Suitable doors not shown are provided forcleaning compartments I9 and 20.

In operation, the invention may be practiced as follows:

The furnace is charged with the material to be treated and the furnaceheated to the proper temperature. For the recovery of zinc from 20 lead,typical substances which may form the charge are raw spelter,galvanizers dross, zinc dross, leady zinc, salvage materials of asimilar nature, and the like. It is generally preferable to introducethe charge into the liquation compartment through charging port 21,although special cases may warrant direct charging to the distillationchamber. Again, the charge may be introduced either in the liquid orsolid state, depending ,upon circumstances.

After melting the charge in the furnace, the respective baths of theliquation and distillation compartments are brought to their appropriatetemperatures. The temperature in the liquation compartment is maintainedat a value slightly above the melting point of the bath, while in thedistillation compartment a sufiicient temperature is maintained toinsure rapid boiling of zinc. It has been found, generally, that atemperature range of from 430 C. to 500 C. is appropriate 40 for theliquation compartment, while operation of the distillation compartmentat temperatures slightly above 900 C. gives excellent results, when aWorking with normal materials at normal atmospheric pressure.

Heat may be supplied to the distillation compartment by means ofsubmerged fire tubes constructed of carborundum, graphite, or similarmaterial which are fired internally with an airfuel mixture employingthe principles of surface combustion. If desired the fire tubes may beanchored for increased mechanical strength. Other heating means may beemployed, but those in which the heat is supplied below the free surfaceof the bath are preferable.

A portion or all of the hot gaseous products of combustion from the firetubes 23 may be conducted through passageway 24 and into the liquationcompartment through port 25 to complete the heat balance in thatcompartment of the furnace. Combustion gases not used for this purposeare vented through flue 26.

To provide intercirculation and exchange between the' liquation anddistillation compartments, suitable ports 2| and 22 are provided in thedividing wall l8. The rate of circulation may be controlled by thenumber, size and location of these connecting ports, thus eliminatingany necessity for employing a pumping scheme or other method of forcedcirculation. The rate of flow may be, of course, controlled by anysuitable mechanism, such for example, by a spindle valve (not shown)located preferably in the upper port.

By reason of the novel furnace design and the method of operationalready described, the bath in the distillation compartment has, at alltimes, actually and relatively, a low lead content. Hence, in operation,zinc vapor substantially free from lead is volatilized and removed fromthe compartment through exit 30, whence it may be condensed to form highgrade zinc metal, burned to produce zinc oxide, or otherwise utilized. v

Unlike ordinary distillation practices in which the ratio of lead tozinc in the bath must necessarily increase as volatilization of the zincprogresses, the present invention continuously maintains a low ratio oflead to zinc inthe bath undergoing distillation. The maintenance of thislow lead value is made possible by the intercirculation and exchangeeffected between the distillation and liquation compartments. As aresult of this circulation, the lead left behind in the distillationcompartment following the volatilization of the zinc is circulated intothe liquation compartment which, as before stated, is substantiallycooler than the distillation compartment. At this lower temperature, thelead is less soluble in the zinc, and, hence, separates out as a liquidwhich collects at the bottom of the compartment because of its higherspecific gravity.

As the zinc content in the furnace is decreased by volatilization andthe lead collected in the bottom of the liquation chamber, additionalcharges of material may be added to the system without interrupting thecontinuous operation of the furnace. As before stated, the charge may beliquid or solid and may be charged to either compartment, although itwill normally be introduced into the liquation compartment. As leadaccumulates in the liquation compartment, it

may be removed at convenient intervals through tap hole 28.

.In order to more clearly illustrate the advantages'of the presentinvention and its mode of operation, the following specific example isset forth:

Zinc containing from 6% to 10% lead with a trace of iron was charged tothe furnace. The liquation compartment was maintained at from 450 C. to500 C., while the distillation compartment was operated slightly inexcess of 900 C., at which temperature volatilization of the zincproceeded rapidly. Samples of the metal taken from the distillationcompartment and the upper stratum of the liquation chamber analyzed3.06% lead, and 3.00% lead, respectively. At the same time, a sampletaken from the bottom of the liquation chamber analyzed 98.3% lead,while the volatilized zinc emerging from the distillation compartmentanalyzed less than 0.003% lead.

As previously stated, it is possible'by the present invention to distillcontinuously zinc vapor from a bath of low lead content and the aboveAnalysis of the distilled Analysis of melt and condensed zinc in theretort Lead, by weight Less than 0. 001 3 Lead, 51 weight Nab- H OM00!0000 arch-mo This table clearly illustrates the well known fact that asthe percentage of lead in a bath from which zinc is being volatilized isincreased, the percentage of lead in the vapor and condensate is alsoincreased. By means heretofore described, the present invention, at alltimes, insures a low lead content in the bath from which the zinc isdistilled and thus makes possible the continuous evolution ofsubstantially pure zinc vapor.

The invention has for an important adaptation the treatment of salvagematerial such as diecastings or scrap containing predominately zinctogether with smaller amounts of other metals, such, forexample, asaluminum, tin, copper and lead, together with other minor When operatingupon such materials, the zinc is boiled off, as described above, and thelead and tin are liquated out. The remaining constituents of the metal,such as the aluminum and copper, and other minor impurities graduallyaccumulate in the bath, and are periodically removed by tapping the bathfrom the furnace.

Various heating means and media may, of course, be employed for both theliquation and distillation chambers. For example, in furnace design,burners have been installed in the liquation chamber for meltingmaterial charged in the solid state.

Again, while the invention has been described with reference to theseparation of lead and zinc,

' it will be appreciated that the method and apparatus of the inventionmay be used to advantage in effecting a large number of separationswherein the appearance of a new phase is produced by change ofthermodynamic environment. Thus, for example, zinc and selenium may besepa rated; also, zinc and bismuth, and zinc and thallium; and also,sodium and magnesium.

While certain novel features of the invention have'been disclosed andare pointed out in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in the art without departing from the spirit of the invention,and that it is intended and desired toembrace within the scope of theinvention such modifications and changes as may be necessary to adapt itto varying conditions and uses.

What is claimed is:

l. The process for separating metals which impurities.

comprises forming a molten'bath thereof, subjecting a portion of suchbath to a temperature sufficient to effect volatilization of one of themetals, simultaneously maintaining the remaining portion of the bath ata temperature suitable for the liquation of the other metal andeffecting intercirculation and exchange between the respective portionsof the bath while conducting said volatilizing and liquating operations.

2. In separating metals which exhibit a single liquid phase at onetemperature but which present an additional phase at a lowertemperature, the improvement which consists in effectingintercirculation and exchange between two baths of such metals whilemaintaining said baths at such different temperatures that distillationof the lower boiling metal is effected in one bath and the other metalis removed from the system by liquation in the other of said baths.

3. The process for separating metals which comprises simultaneouslysubjecting different portions of a bath of the metals to distillationand liquation while effecting circulation and exchange between saidportions.

4. The process for obtaining substantially pure zinc vapor from zinccontaminated with lead.

which comprises subjecting such metal to a temperature slightly inexcess of 900 C. thereby volatilizing zinc while continuously effectingintercirculation between such metal and a body of similar metalmaintained at a temperature of from 430 to 500 C., thereby maintainingthe lead content of the metal at the higher temperature at a low value.

5. The process for treating a metal containing zinc and lead whichcomprises charging such metal to a furnace having liquation anddistillation compartments,.establishing intercirculation and exchange ofmetal between said compartments, and operating the furnace in a mannercalculated to maintain the metal in the liquation and distillationcompartments at temperatures of from 430 to 500 C. and slightly inexcess of 900 C., respectively.

6. The method of treating zinc containing lead which comprisesestablishing a molten bath thereof, subjecting a portion of such bath totemperatures sufiicient to effect volatilization of zinc, simultaneouslymaintaining the remaining portion of the bath at a temperature suitablefor the liquation of lead from zinc and effecting intercirculation andexchange between the respective portions of the bath during saidvolatilizing and liquating operations.

7. The process for separating zinc from lead which comprisessimultaneously subjecting different portions of a bath of these metalsto distillation and liquation while effecting circulation and exchangebetween said portions.

8. The process for treating zinc contaminated with lead which comprisessubjecting a first portion of a molten bath thereof to distillationwhile subjecting a second portion of said bath to liquation andsimultaneously effecting intercirculation and exchange of metal betweensaid first and second portions.

9. The process for refining spelter which comprises applying suificientheat below the free surface of a bath thereof to distill the zinc andmaintaining the lead content of the bath at a constantly low value asthe distillation progresses.

10. In the production of high grade zinc by distillation from zinccontaminated with lead, the improvement which consists in maintainingcirculation between the metal undergoing distillation and a similar bathof metal. maintained at a temperature suitable for liquation of leadfrom zinc thereby constantly maintaining the lead content of the metalundergoing distillation at a low value.

11. The process for producing high grade zinc from zinc contaminatedwith lead which consists in heating a bath of such metal below the freesurface thereof to a temperature suiiicient to effect removal of zinc asvapor and simultaneously effecting intercirculation of metal betweensaid bath and a similar bath of metal maintained at a temperaturefavoring the liquation of lead from zinc.

12. The process for treating salvage material such as die-castings orscrap containing predominately zinc together with smaller amounts ofaluminum, tin, copper and lead and other minor impurities whichcomprises forming a molten bath thereof, subjecting a portion of suchbath to a temperature sufficient to effect boiling of the zinc,simultaneously maintaining the remaining portion of the bath at atemperature suitable for liquation of the lead and tin, the aluminum andcopper remaining in the bath, and effecting intercirculation andexchange between the respective portions of the bath.

13. The process for treating salvage material such as die-castings orscrap containing predominately zinc together with smaller amounts ofaluminum, tin, copper, and lead and other minor impurities whichcomprises forming a molten bath thereof, subjecting a portion of suchbath to a temperature sufficient to effect boiling of the zinc,simultaneously maintaining the remaining portion of the bath at atemperature suitable for liquation of the lead and tin, effectingintercirculation and exchange between the respective portions of thebath, allowing the remaining metals to accumulate in the bath andperiodically removing accumulated portions of the bath to remove thecontaminating metals contained therein.

MELVIILE F. PERKINS.

